The invention relates to a composite casting for the charging and controlled addition of pre-alloys to molten alloys of room-temperature-reactive and -nonreactive metals contained in a crucible.
An example of an alloy of room-temperature-reactive and -nonreactive metals is an aluminum alloy containing about 3 percent of lithium by weight, in which other alloy elements such as magnesium, for example, may also be contained. Such alloys are important in aviation, because they reduce the weight of aircraft accordingly, so that the saving in fuel costs over the total life of the aircraft is several times greater than the additional cost of such an alloy.
In the transformation of such alloys to sheets, extrusions and rough castings, waste is produced to a considerable degree, and when defective pieces are returned they constitute scrap. Both the wastes and the scrap are put through a recycling process in which melting plays an important part. In the melting, the reactive metals--lithium for example--tend to evaporate, and the metal being worked will not have in every case the prescribed content of the reactive alloy elements. In this case the basic metal--aluminum for example--must be treated with a greater percentage of the reactive metal.
If lithium has to be added, the storage and handling of this metal is complicated, because alloys containing more than 6 to 8 percent of lithium by weight are decidedly reactive even at room temperature, so that such alloys are no longer easy to handle. To compensate lithium losses in recycling it is very desirable to use pre-alloys whose lithium content is definitely greater than 3 percent by weight.
The invention is addressed to the problem of devising a method of the kind described in the beginning, in which pre-alloys are used which have a reactive metal content which is decidedly greater than the content of the reactive metal in the melt or in the end product, without any tendency on the part of the pre-alloy in question to react with the ambient air at room temperature.